Inhibition of Increase and Activity of Tobacco-Mosaic Virus Under Nitrogen-Deficient Conditions

Abstract

IntroductionAlthough viruses eause many plant diseases, little is known regarding their metabolism since they apparently multiply only in living tissue. Here it is difficult to differentiate between the metabolism of a host and that of a pathogen. Multiplication of viruses in vito is a well recognized fact and thermal inactivation in vivo of a few viruses has been definitely established. No other method for the inactivation of virus in vivo has been demonstrated experimentally.In this study on virus metabolism, a knowledge of the nitrogen metabolism of normal tobacco plants and the discovery that nitrogen supplied to a virus-infected plant had an effect on virus concentration (19) have made it possible to distinguish to some extent between the anabolic and katabolic processes involved. It is well known (14, 24) that in mature leaves of a nitrogen-deficient plant proteins are hydrolyzed and proteolytic decomposition products liberated. These are translocated to the growing point where they supply the meristem with materials necessary for protein svnthesis. A studv of the effect of withholding nitrogen from a tobacco plant diseased with tobacco mosaic on the total quantity and specific biological activity of virtus within the plant has thrown light on the following questions: Is 24th day the nitrogen-fed plants were nearly 5 times the size of those deficient in nitrogen. During this 24-day period, the green weight of nitrogenfed plants increased about 18-fold, whereas that of nitrogen-deficient plants increased less than 4 times. A portion of this increase in nitrogen-deficient plants was probably due to the reserve of unassimilated nitrogen present in these plants at the time they were transferred to the minus-nitrogen treatment. SPENCER: TOBACCO-MOSAIC VIRUS AND NITROGEN DEFICIENCYData pertaining to the total-protein content andl the virus-protein content of aliquots of juice from the two sets of plants at each harvest are recorded in table III. In plants receiving nitrogen, the mg. of total protein per ml. of juice increased at first and then decreased slightly. The lowv protein contents recorded on the 16th and 24th day were probably due in part to the fact that each of these harvest days was preceded by one or more dark, cloudy days. The decrease in carbohydrate synthesis is accompanied by an accelerated hydrolysis of stored proteins. In

Review of Recent Work on Nitrogen Metabolism

“…Rishkov & Smirnova (1939) report that virus formation in tomato plants is unaffected by nitrogen starvation. This is contradicted by Spencer (1941), whose nitrogen-deficient tomato seedlings had constant contents of virus and total protein over a period when both increased fivefold in controls with adequate nitrogen. He found that virus protein was not utilized in severe nitrogen deficiency.…”

The Preparation and Use of Tobacco Mosaic Virus Containing Radioactive Phosphorus

“…A solution containing 51 rag. of disodium phosphate and 0.25 miUicuries of radioactivity was added to 4 pots containing medium-sized mosaic-diseased Turkish tobacco plants which had been grown in sand and fed with a complete nutrient solution as described by Spencer (1). After 48 hours, the plants were removed, their roots well washed, and the entire plants frozen.…”

“…Then each of 3 normal and 3 diseased plants from this group was fed 50 ml. of a nutrient solution prepared by adding 330 mg. of disodium phosphate containing 7 millicuries of radioactivity to 20 liters of the complete nutrient solution described by Spencer (1). The remaining diseased and normal plants were fed a nutrient solution prepared by adding 330 mg. of ordinary disodium phosphate to 20 liters of the complete nutrient solution.…”

Influence of Nitrogen Supply on the Rate of Multiplication of Tobacco-Mosaic Virus

“…In a former paper the writer (10) reported experiments which showed that the virus activity of juice expressed from tobacco plants diseased with tobacco mosaic was correlated with the amount of nitrogen supplied to the plants. No conclusions could be drawn from these experiments as to whether this increased activity was due to an increase in the rate of virus multiplication or to some other factor, such as greater accumulation of virus particles over a longer period of time, less destruction of virus, or greater dispersion of aggregates of virus particles.…”

“…of nutrient solution every other day and was supplied with water whenever necessary between nutrient applications. Low, medium, and high levels of nitrogen were maintained by the use of nutrient solutions, the composition of which has been described previously (10). As in the earlier work, the solutions were all supplemented with boron and manganese, as HI3BO3 and MnSO4 2H2O, respectively, at a concentration equivalent to 0.5 p.p.…”